There are a variety of rolling mills for rolling a steel plate etc., of which categories differ depending on the number of rolling rolls per stand. What the present invention is applied to, is a rolling mill including at least a pair of backup rolls disposed up and down. The following discussion will concentrate on a four-high rolling mills including a pair of work rolls and a pair of backup rolls.
A roll eccentricity of the rolling mill may be a large disturbance to control of a thickness of the strip or to tension control. Principal factors for causing the roll eccentricity are:
(a) an influence of a bearing key of the backup roll, PA1 (b) a bias of an axial core of the backup roll, and PA1 (c) ill-formed roundness of the work roll.
The eccentricity caused by the factor (a) among these factors, it is conceived, has the largest eccentric quantity.
A variety of methods of reducing the roll eccentricity in a control-based manner have been proposed and applied to a multiplicity of rolling plants. A typical method thereof is disclosed in JP 51-138468 A. According to this method, a rolling force signal detected corresponding to a rotational angle of the backup roll is Fourier-transformed, then a frequency component synchronizing with the rotation of the backup roll is extracted, and a roll gap is controlled by use of this frequency component.
Based on this prior art method, a rolling force generated by rotating and making the up-an-down rolls contact with each other in a non-rolling state, i.e., by performing a so-called kiss-roll, is detected and Fourier-transformed, thereby detecting a roll eccentricity. This method may be said to have a high detection accuracy because of only the roll eccentricity appearing in a rolling force signal generated. With a progress of rolling process, however, a state of the rolls might change, and hence a requirement for adopting this method is that the kiss-roll can be easily done in order to respond to that change. This method is therefore hard to be applied to a tandem rolling mill incapable of easily performing the kiss-roll, and it is, if applied, difficult to attain high-accuracy control.